Sahih al-Bukhari, Hadith 3564 ⓘ
Narrated `Abdullah bin Malik bin Buhaina Al-Asdi: When the Prophet prostrated, he used to keep his arms so widely apart that we used to see his armpits. (The sub-narrator, Ibn Bukair said, "The whiteness of his armpits.")
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا بَكْرُ بْنُ مُضَرَ، عَنْ جَعْفَرِ بْنِ رَبِيعَةَ، عَنِ الأَعْرَجِ، عَنْ عَبْدِ اللَّهِ بْنِ مَالِكٍ ابْنِ بُحَيْنَةَ الأَسْدِيِّ، قَالَ كَانَ النَّبِيُّ صلى الله عليه وسلم إِذَا سَجَدَ فَرَّجَ بَيْنَ يَدَيْهِ حَتَّى نَرَى إِبْطَيْهِ. قَالَ وَقَالَ ابْنُ بُكَيْرٍ حَدَّثَنَا بَكْرٌ بَيَاضَ إِبْطَيْهِ.
also referenced under: Book 61, Hadith 74 (In-Book) & Volume 4, Book 56, Hadith 765 (USC-MSA)